Chazal (Men. 110) derive from the extra words "Zos toras ha'olah..." that learning the parsha of korban olah is equivalent to actually offering the korban. (It seems from the gemara that the same is true for all korbanos. I am surprised that the Ksav Sofer makes a point here of explaining why the principle is applicable specifically to the olah -- since the olah is brought to be mechapeir on hirhurei aveirah, bad thoughts, not bad deeds, therefore, in this case specifically reading and thinking about the parsha can serve as a mechapeir in lieu of the actual korban.) This is why when we read the parshiyos of korbanos in the morning (or the mishnayos in aizehu mekoman) we recite a ye'hi ratzon asking Hashem to count that recitation as a substitute for the korban itself.
The Tur writes that the exception to the above rule is the korban chatas. There is no such thing a a voluntary korban chatas (a korban nedava) -- if you are not obligated to bring a chatas and offer one anyway, it's an issur of chulin b'azarah. You can't say, "Y'hi ratzon that this should count as a chatas," because you may not really be obligated to bring one (the Tur was generous in his opinion of us all).
The Beis Yosef questions the Tur's logic. Chazal tell us that the recitation of the parshiyos of korbanos count as if they were actually offered -- they don't say that the recitation of the ye'hi ratzon counts as if the korbanos were offered. If the Tur was really worried about the problem if chulin b'azarah, then he should recommend omitting the entire parsha of chatas, not just the ye'hi ratzon.
The Beis Yosef answers that reciting the parsha alone counts as a "kaprah b'miktzas" -- whatever that means. It sounds like the Beis Yosef wants to have his cake and eat it too -- he wants the parsha count for something, yet not count enough to pose a chulin b'azarah problem. The Bach has a different twist. He answers that just reading the parsha is a way of hedging one's bets. At the end of the day, the parsha of chatas is still a parsha in chumash. If one is not obligated to bring a chatas, then reading the parsha counts as no more than talmud Torah; if one is obligated to bring a chatas, then it counts as an actual offering of the korban. However, you can only hedge so long as you don't recite the ye'hi ratzon. Once you daven for Hashem to accept the recitation of the parsh as a substitute for the actual korban, all bets are off -- if you ask for the parsha to count as a korban, it counts as a korban.
Why does the Bach's answer make any better sense than the Tur? It seems like we are back to square 1 -- according to the Bach, it's the ye'hi ratzon that triggers the acceptance of the parsha as a korban, but the gemara clearly says that the parsha itself is the substitute!?
Rav Tzvi Pesach Franks (Har Tzvi O.C. 1) uses this question an an opportunity to discuss the concepts of hashgacha and tefilah. He sets down the following principle: Whatever a tzadik asks for, Hashem will deliver, irrespective of whether Hashem knows the request is for the good or for the bad. For example: David haMelech davened that Hashem should test him. Hashem certainly knew that David would fail, but since David asked, he got what he wanted. "Retzon ye'rei'av ya'aseh v'es shavasam yisma v'yoshi'eim" -- it's not double-language in the pasuk, but two seperate points: "Retzon ye'rei'av ya'aseh," Hashem does the will of the Righteous, even though He knows it will not turn out the way they think it will; "V'es shavasam yishma v'yoshi'eim," and after the fact, when the tzadikim realize the hole they dug for themseves and daven for Hashem's help to get out of it, He listens and responds. Be careful what you ask for as you may just get it.
As you don't say the ye'hi ratzon, Hashem does what's best -- if you need a korban chatas as a kaparah, He counts the reading of the parsha as a korban; if not, He counts it as talmud torah. However, once you ask Hashem to count the parsha as a korban, even if that works to your detriment, even if that results is chulin b'azarah, Hashem will grant your request and the damage is done.
I would add one final point. The Bach doesn't just say that tzadikim should avoid saying the ye'hi ratzon because Hashem will act on it -- he says everyone, you and me included, should avoid saying it. I don't think this is b'geder lo plug; I think we see from here that we have every right to assume that Hashem listens and responds to our tefilos. Puk chazei how people talk about tefilah -- it's not uncommon for people to ask why Hashem didn't listen to their prayers without giving a moment's thought to the audacity it takes to assume that the Master of the Universe should pay attention and respond to a sin-filled basar v'dam regardless of his/her past history! The fact that such an assumption comes as second nature to us perhaps is not just because we like to delude ourselves as to our own importance, but rather it reflects an underlying truth about the nature of tefilah and hashgacha.